Rheostat assembly



Feb- 2, 1965 R. w. BEMMANN r-:TAL 3,153,719

RHEOSTAT ASSEMBLY Filed Nov. 5, 1962 I NVEN TOR` United States Patent Office 3,168,719 Patented Feb. 2, 1965 3,168,718 RHEOSTAT ASSEMBLY Richard W. Bemmann and Werner F. Schultz, Flint, Mich., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Nov. 5, 1962, Ser. No. 235,450 4 Claims. (Cl. 2338-165) This invention relates to a rheostat assembly and more particularly to a novel construction thereof.

In certain rheostat applications such as those which require a rheostat to be mounted on a printed circuit board it may be desirable that the rheostats components be minimum in number and compactly assembled within a housing member. It may also be desirable that a cooperating cover member be provided for the housing member and which members together serve as structural supports for the rheostats components. Furthermore, it may be desirable that means be provided for fastening the cover member to the housing member in a manner to insure maintenance of an electrical circuit between the output terminals of the rheostat when the resistance is being adjusted or when the rheostat is subjected to shocks and vibrations.

In accordance with this invention, a rheostat is provided having a minimum number of compactly assembled components including a resistance element mounted within a housing member. A movable member is movably mounted within the housing member and includes an electrical contact on one side thereof in slidable engagement with the resistance element. The movable member also includes an electrical resilient Wiper arm on its other side electrically connected with the contact. A cover member including a conductive portion is fastened to the housing member in such a manner that the conductive portion engages the wiper arm and urges the contact into engagement with the resistance element. Accordingly, an electrical circuit is maintained between a terminal connected with the resistance element and a terminal connected with the conductive portion of the housing member when the rheostats resistance is being adjusted and when the rheostat is subjected to shocks and vibrations.

A more complete understanding of this invention may be had from the detailed description which follows taken with the accompanying drawing in which:

FIGURE 1 is a plan View illustrating one embodiment of the invention mounted on a printed circuit board;

FIGURE 2 is a cross-sectional view taken along line 2-2 in FIGURE 1 looking in the direction of the arrows;

FIGURE 3 is a cross-sectional view taken along line 3- 3 in FIGURE 2 looking in the direction of the arrows;

FIGURE 4 is an exploded perspective view of one embodiment of the invention.

Referring now to the drawings there is illustrated in FIGURE k1 one embodiment of the rheostat assembly mounted on a printed circuit board 10. The construction of the rheostat assembly will be more readily understood with respect to FIGURES 2, 3 and 4 wherein it is seen that the assembly comprises a non-conductive substantially rectangular cup-shaped housing members 12. The housing member 12 may be molded from any suitable plastic material so as to obtain a rigid cup-'shaped structure.

A pair of identical wire wound resistance elements 18 and 2l) are provided, each comprising a flat rectangular shaped insulator board 22 having a suitable length of resistor wire 24 wound thereon, Brass terminals 26 and 28 are respectively mounted at one end of the resistance elements 18 and 20 and protrude therefrom in the manner as shown in FIGURE 4.

The inner surface of the closed end of the housing member 12 has formed therein two recesses 30 and 32 terminating in rigid surfaces 34 and 36, respectively. The contours of the recesses 30 and 32 are formed so as to respectively conform with the contours of the resistance elements 18 and 2l). The resistance elements 18 and 20 are mounted in the recesses 30 and 32, respectively, as shown in FIGURES 2 and 3 so that the contours of the resistance elements and the respective recesses are in alignment to thereby retain the elements in spaced relationship with respect to each other. In addition, the recesses 30 and 32 are so formed that with the resistance elements mounted therein the terminals 26 and 28 are disposed from each other at opposite ends of the recesses and protrude outwardly of the housing member 12 for reasons as will be explained hereinafter.

At the geometric center of the closed end of the housing member 12 there is provided a circular recess 42 in the inner surface of the member 12 in the spacing between the recesses 3() and 32. A pair of boss members 38 and 40 are formed in the inner surface of the housing member 12, each being equidistant from the recess 42 and protruding outwardly from the spacing between the recesses 30 and 32.

A non-conductive disc shaped rotor member 44 is provided having two opposing sides. A pair of spaced resilient wiper arms 46 and 48 constructed of conductive material are mounted diametrically opposite each other on one side of the rotor member 44. A pair of electrical contacts 50 and 52 are mounted on the other side of the rotor member 44 adjacent to and electrically connected with the wiper arms 46 and 48, respectively. A rectangular slot 54 is provided in the rotor member 44, bisected by the geometric center of the rotor member 44 and has an extent corresponding to the diameter of the circular recess 42 in the closed end of the housing member 12. A pair of arcuate grooves or slots 56 and 58 are provided in the rotor member 44 diametrically opposite each other. The radius of each of the arcuate slots 56 and 58 is equal to one half the distance between the boss members 38 and 40. The width of the slots 56 and 58 is suicient to receive the boss members 38 and 40, respectively. The rotor member 44 is mounted within the housing member 12 so that the contacts 50 and 52 engage the resistance elements 18 and 20, respectively, and that the boss members 38 and 40' are respectively received by the arcuate grooves 56 and 58. The arcuate slots 56 and 58 serve to guide and limit rotative movement of the rotor member 44 in accordance with the radius and extent, respectively, of the arcuate slots. The boss members 38 and 40 and the arcuate slots 55 and 53 are preferably located in the spacing between the recesses 30 and 32 and in the rotor member 44, respectively, so that the contacts 50 and 52 are prevented from engaging the resistance elements 28 and 18, respectively.

A nonconductive substantially rectangular shaped cover member 60 is provided having two opposing sides. A pair `of spaced conductive plates 52 and 64 are mounted on one side of the cover member 6) corresponding in extent to the `arcuate paths respectively traced by the wiper arms 45 and 48 as the contacts Sti and 52 slidably engage the resistance elements 18 and 20, respectively. A pair of electrical terminals 66 and e8 are respectively mounted on the conductive plates 62 and 64 and protrude therefrom through the other side of the cover member 60. A pair of notches 70 and 72 are formed in the periphery of the cover member 60 and are of suiiicient size to receive the terminals 26 and 28, respectively. A circular slot 74 is formed in the cover member 60 at the geometric center thereof and has a diameter in excess of the extent of the rectangular shaped slot 54 in the r0- tor member 44.

In the assembly as shown in FIGURE 2, fastening means are provided for securely snap-fitting the cover member 69 to the housing member 12 and include a lifp portion 76 formed in the inner surface of the housing member 12 at the open end thereof. This permits alignment of the geometric centers of the closed end of the housing member `12, the rotor member 44 and the cover member 60. The notches 7@ and 72 in the cover member 60 receive the terminals 26 and 28, respectively, permitting the terminals to protrude through the cover member 60. In addition, the snap lit of the cover member 69 on the housing member 12 is such that the conductive plates 62 and 64 frictionally engage wiper arms 46 and 48, respectively, so as to respectively urge the contacts 50 and 52 into frictional engagement with the resistance elements 18 and 2t) against the resiliency of the wiper arms. Thus the Wiper arms permit the assembly to insure maintenance of `an electrical circuit from the terminal 26 to the terminal 66 via the resistance element 18, the contact 50, the wiper arm 46 and the conductive plate 62 when the resistance is being adjusted and when the assembly is subjected to shocks and vibrations. Similarly, the assembly insures maintenance of an electrical circuit from the terminal Z8 to the teminal 68 via the resistance element 20, the contact 52, the wiper arm 48 Vand the conductive plate 64.

The rheostat assembly permits simultaneous adjustment of resistance between the terminals 26 and 66 and between the terminals 2S and 68 in a readily accessible manner. This may be accomplished by inserting an adjustment member such as a screwdriver through the circular slot 74 in the cover member 69 so as to engage the tool portion of the screwdriver with the rectangular slot 54 in the rotor member 44. The circular recess 42 in the housing member 12 serves to guide rotative movement of the tool portion of the screwdriver. If the operator rotates the screwdriver and hence the rotor member` 44 in a given direction with respect to the resistance elements 13 and 20 the amount of resistance between the contact 50 and the terminal 26 Will vary in the same amount as that between the contact 52 and the terminal 2S.

A further feature of the rheostat assembly is the provision of retaining means for mounting a fixed resistor on the'exterior of the housing member 12. This is accomplished by providing a groove 78 in the outer surface of the housing member 12 at the closed end thereof. A pair of resilient arms 80 and 82 are mounted on the exterior of the housing member 12 and are disposed from each other on opposite sides of the groove 7S and are adapted to receive the body portion of a fixed resistor. U-shaped resilient terminal holding means 86 and 8S are mounted on the exterior of the housing member 12 at the open end thereof. A fixed resistor 90 is provided having a body portion 92 and a pair of terminals 94 and 96 protruding at opposing ends thereof. The body portion 92 of the resistor 9G is securely mounted in the groove 78 by means of the resilient arms 80 and 82 and the terminals 94 and 96 are wrapped about the exterior Vof the housing member 12 and held in place by the U- shaped resilient holding means 86 and S8, respectively, so that the terminals 94 and 96 extend beyond the open end of the housing member 12.

The composite rheostat assembly as shown in FIGURE V2 with the terminals 94 and 96, the terminals 26 and 66,

and the terminals 2S and 68 all protruding beyond the open end of the housing member 12 is readily adapted to be mounted on the printed circuit board 1t). The aS- sembly provides a pair of ganged variable resistors and a fixed resistor all in one readily accessible module which permits simultaneous adjustment of the variable resistors.

Although the description of this invention has been given with respect to a particular embodiment, it is not t be construed in a limiting sense. Numerous variations and modifications within the spirit and scope of the invention will now occur to those skilled in the art. For

a definition of the invention, reference is made to the appended claims.

We claim:

l. In a rheostat assembly, the combination comprising a non-conductive cup shaped housing member, first and second resistance elements, the inner surface of the housing member including first and second spaced non-conductive retaining means respectively contoured to c011- form with the contour of the first and second resistance elements, the `first and second resistance elements being mounted within the housing member by the first and second retaining means, respectively, so that the contours of the resistance elements and the contours 'of the respective retaining means are in alignment to thereby retain the resistance elements in spaced relationship with respect to each other, a non-conductive rotor member having first and second spaced contacts mounted on one side thereof and first and second spaced resilient electrical wiper arms mounted on the lother side thereof, the first and second wiper arms being electrically connected with the first and second contacts, respectively, the rotor member being rotatably mounted within the housing member adjacent the resistance elements with the first and second contacts in slidable engagement with the first and second resistance elements, respectively, a non-conductive cover member disposed adjacent the rotor member and including rst and second spaced conductive portions, first and second terminal means electrically connected with the first and second vresistance elements, respectively, and third and fourth terminal means electrically connected with the first and second conductive portions, respectively, of the cover member, fastening means on the housing member urging the cover member toward the rotor with the first and second resilient wiper arms in respective engagement ywith the first and second conductive portions so as to respectively urge the first and second contacts into engagement with the first and second resistance elements.

2. In a rheostat assembly, the combination comprising a non-conductive cup shaped housing member, first and second wire wound resistance elements each having a terminal electrically connected therewith at one end and protruding therefrom, the inner surface of the housing member having formed therein first and second recesses conforming in contour with the contour of the first and second resistance elements, respectively, the first and second resistance elements being mounted in the housing member within the first and second recesses, respectively, so that the contours of lthe resistance elements and the respective recesses are in alignment to thereby retain the resistance elements in spaced relationship with respect to each other so that the terminal of each resistance element protrudes outwardly of the housing member, a boss member mounted to the inner surface of the housing member and protruding outwardly therefrom in the spacing between the first and second recesses, a non-conductive rotor member having first and second spaced contacts mounted on one side and first and second spaced resilient electrical Wiper arms mounted on the other side electrically connected with the first and second contacts, respectively, the rotor member defining an arcuate slot therein adapted to receive the boss member, the rotor member being rotatably mounted Within the housing member with the first and second contacts respectively in slidable engagement with the first and second resistance elements and with the boss member received by the arcuate slot in the rotor member so as to thereby guide and limit rotative movement of the rotor member in aC- cordance with the radius yand extent, respectively, of the arcuate slot, the terminals of the resistance elements being located at opposite ends of the resistance elements so that rotative adjustment of the rotor member with respect to the resistance elements in a given direction will change the amount of resistance between the first contact and therst terminal in the same manner as that between the second contact and the second terminal, a nonconductive cover member including iirst and second spaced conductive portions on one side thereof respectively corresponding in extent to the arcuate paths traced by the first and second Wiper arms as the irst tand second contacts slidably engage the tirst and second resistance elements, respectively, each of the tirst and second conductive portions of the cover member having a terminal electrically connected therewith and protruding therefrom through the other side of the cover member, the cover member defining a pair of notches therein each adapted to receive a dierent one of the terminals of the tiret and second resistance elements, fastening means on the housing member urging the cover member toward the rotor member With each of the terminals of the irst `and second resistance elements protruding through a different one of the notches in the cover member and with the iirst and second resilient wiper arms in respective engagement with the `first and second conductive portions so as to respectively urge the iirst and second contacts into engagement with the i'irst and second resistance elements, resistor retaining means on the exterior of the housing member, and a fixed resistor having a pair of terminals mounted on the exterior of the housing member by the resistor retaining means so that each terminal of the resistor extends beyond the cover member.

3. A rheostat assembly comprising a cupshaped housing member, vrst and second resistance elements mounted in said housing in spaced relationship with respect to each other, :a non-conductive rotatable rotor member rotatably supported by said housing member and having iirst and second spaced contacts mounted on one side thereof and electrically connected -with iirst and second spaced resilient wiper arms mounted on the other side thereof, a nonconductive cover member including rst and second spaced conductive portions, rst and second terminal means electrically connected with the irst and second resistance elements respectively, and third and fourth terminal means electrically connected with the first and second conductive portions respectively of the cover member, fastening means in the housing member for receiving the cover member and maintaining the first and second wiper arms in engagement with the itirst and second conductive portions respectively and the :first and second contacts in engagement with the iirst and second resistance elements respectively Whereby rotation of said rotor member simultaneously varies the resistance between said first and third terminal means and said second and fourth terminal means.

4. In a rheostat assembly comprising a housing member, first and second resistance elements supported in said housing in spaced relationship -with respect to each other, a rotatable rotor member having iirst and second spaced contacts on one side thereof electrically connected with a pair of spaced resilient wiper arms on the other side thereof, means forming an integral vpart of said housing for both positioning said rotor in said housing and limiting rotational movement between said rotor and said housing, a non-conductive cover member adapted to be releasably received by said housing and including a pair of conductive portions -on one side thereof in engagement with said Wiper arms for urging said first and second contacts into engagement with said first and second resistance elements respectively, a terminal extending yfrom each of said resistance elements and from each of said conductive portions lwhereby rotation of said rotor simultaneously changes the resistance between the terminals of each of the conductive portions and a corresponding terminal of the resistance elements.

References Cited in the file of this patent UNITED STATES PATENTS 2,477,711 Youhouse Aug. 2, 1949 2,577,108 Coyne et al. Dec. 4, 1951 2,706,760 Mucher Apr. 19, 1955 2,899,662 Berden et al Aug. 1l, 1959 2,934,734 Wolfe Apr. 26, 1960 3,072,872 OShea Jan. 8, 1963 

1. IN A RHEOSTAT ASSEMBLY, THE COMBINATION COMPRISING A NON-CONDUCTIVE CUP SHAPED HOUSING MEMBER, FIRST AND SECOND RESISTANCE ELEMENTS, THE INNER SURFACE OF THE HOUSING MEMBER INCLUDING FIRST AND SECOND SPACED NON-CONDUCTIVE RETAINING MEANS RESPECTIVELY CONTOURED TO CONFORM WITH THE CONTOUR OF THE FIRST AND SECOND RESISTANCE ELEMENTS, THE FIRST AND SECOND RESISTANCE ELEMENTS BEING MOUNTED WITHIN THE HOUSING MEMBER BY THE FIRST AND SECOND RETAINING MEANS, RESPECTIVELY, SO THAT THE CONTOURS OF THE RESISTANCE ELEMENTS AND THE COUNTROUS OF THE RESPECTIVE RETAINING MEANS ARE IN ALIGNMENT TO THEREBY RETAIN THE RESISTANCE ELEMENTS IN SPACED RELATIONSHIP WITH RESPECT TO EACH OTHER, A NON-CONDUCTIVE ROTOR MEMBER HAVING FIRST AND SECOND SPACED CONTACTS MOUNTED ON ONE SIDE THEREOF AND FIRST AND SECOND SPACED RESILIENT ELECTRICAL WIPER ARMS MOUNTED ON THE OTHER SIDE THEREOF, THE FIRST AND SECOND WIPER ARMS BEING ELECTRICALLY CONNECTED WITH THE FIRST AND SECOND CONTACTS, RESPECTIVELY, THE ROTOR MEM- 